I have to agree that it's the teacher(s) that makes all the difference! My DD5 and DD4 went to Montessori school last year (2-3 and 4 years old at the time) and had great experiences. Although I have to say DD4's teacher never noticed she was GT (the assist. teacher did) I had to ask for more challenging materials to be put in to the toddler room and they happily did that. Since she was only 2 and in a toddler room, I didn't think it was a big deal. I was happy with the social skills she was developing and she loved school, which meant that she wasn't bored and the classroom was well structured (she HATES disorder!) DD5 had a great preschool year and a wonderful teacher.
We moved, DD5 has transitioned nicely into a public school K. I found a local (certified)Montessori for DD4 and checked it out thoroughly, meeting w/preschool teachers for over an hour. She seemed happy there, but as the year progressed, she was not being challenged again. On a classroom visit, DD4 told me there were certain materials that were only for the K kids. I thought she had misunderstood so I went to the teachers to clear it up. To my shock, they said she was correct. She wants to use the large number chains but is being denied because they don't think she's "ready". There are other problems popping up and she won't be returning there next year. I absolutely love the philosophy, but again it's the teacher that matters!